The present invention relates to a system for monitoring and protecting a vehicle hydraulic system.
Serious damage can result when a drivetrain in a tractor is not operated at a proper operating temperature, with a proper clutch engagement pressure or with proper lubrication. Therefore, various systems have been used to protect transmissions from such conditions. For example, gages have been used to display conditions to an operator so that the operator could take appropriate action if the transmission oil temperature became higher than a threshold or if system pressure drops below a threshold. Some gages are augmented with flashing lights or audible alarms.
Another approach is a xe2x80x9cMurphy switchxe2x80x9d which automatically shuts an engine down if transmission oil temperature becomes higher than a threshold or if system pressure falls below a threshold.
The hydraulic system pressure level is set so that engaged transmission clutches will not slip even when transmitting full engine torque. Hydraulic system pressure is set by a pressure regulating valve. The pressure regulating valve ensures that system pressure remains above a set level even under low pump flow conditions, as is the case when the tractor is running at low idle. A system which monitors system hydraulic pressure with respect to a single warning level may be sufficient to prevent transmission clutch slippage and large hydraulic system leaks, but it may not detect low to medium sized hydraulic leaks which may result in a loss of lubrication fluid. In order to detect a full range of hydraulic leaks, the lube system needs to be monitored. However, monitoring lube pressure with respect to a single pressure level would be unsatisfactory because a transmission lube circuit will normally operate under low pressure conditions, not just when little or no lube oil is available. For example, normal lube pressure is low when the lube oil is warm and engine speed is low. Thus, using low lube pressure as a warning level will not detect leaks when the engine speed is operating at higher speeds.
A known system, marketed by Case, detects critically high engine and transmission temperature and low engine oil pressure, and shuts down the engine if these parameters are above certain thresholds.
U.S. Pat. No. 4,489,305, Lang, et al., issued in 1984 and is assigned to the assignee of this application. The Lang et al. patent describes a monitoring system for a vehicle, such as an agricultural tractor, which includes a hydraulic assist-type transmission with fluid control and lubricating circuits. The monitoring system senses the fluid pressure in the lubricating circuit, the hydraulic fluid temperature and the engine speed. The sensed pressure is compared to a temperature and engine speed-compensated alarm value. Alarm signals are generated when the sensed pressure is continuously below the alarm value for a certain period. The alarm is disabled when the engine speed falls below a non-zero threshold level. However, this system and the previously mentioned systems do not automatically shut off any hydraulic functions to determine the source of the leak, nor does it isolate or lock-out only the hydraulic function(s) that are determined to be the cause of the leak and any other affected hydraulic functions.
Accordingly, an object of this invention is to provide a system which detects and protects against small and medium size oil leaks in vehicle hydraulic systems.
A further object of the invention is to provide such a system which also determines which vehicle system is the source of the problem while the vehicle is in operation without the operator having to place the vehicle into a special mode.
A further object of the invention is to provide such a system which is responsive to recent operational status of the transmission or of other hydraulic functions to aid in determining which vehicle system is the source of the problem.
A further object of the invention is to deactivate (lock-out) only the hydraulic element(s) found to be causing a leak and any other hydraulic elements affected by the leak, while allowing all other non-affected hydraulic functions of the tractor to remain operational.
A further object of the invention is to automatically engage a limp home mode under certain low lube conditions.
These and other objects are achieved by the present invention, wherein a system and method are provided for monitoring a vehicle hydraulic system having a plurality of hydraulic function elements. The hydraulic system includes a hydraulic pump for supplying pressurized hydraulic fluid to the plurality of hydraulic function elements via a corresponding plurality of hydraulic element control valves, an electronic control unit for controlling the element control valves. The pump also supplies lube fluid to a lubrication circuit via a lube line if requirements of the hydraulic function elements are met. The method includes sensing a lube pressure of lube fluid in the lube line, and comparing the lube pressure to a threshold pressure. If the sensed lube pressure is less than threshold pressure, then actively engaged hydraulic elements are tested by disengaging the elements in a predetermined manner while the vehicle is in operation, checking to see if the sensed low lube pressure condition is eliminated. If the sensed low lube pressure condition is eliminated after disengaging an element, then the leaking hydraulic function element (the last element disengaged) is deactivated (locked-out) and a corresponding message is generated and stored. By locking-out the leaking hydraulic function element, lube pressure is returned to normal allowing all non-affected hydraulic function elements on the tractor to remain operable. In many cases, this would allow the operator to continue operating the tractor for the rest of the day until taking the tractor to the dealer for service. If after testing the previously engaged hydraulic elements, the sensed lube pressure is still below threshold pressure, then all elements are deactivated and a limp home mode is automatically enabled. Limp home mode allows the tractor to only be driven in a pre-selected forward or reverse gear. This allows the tractor to be driven onto a truck or to the dealer for service. The pre-selected forward and reverse gear is chosen so that the bearings in the transmission are moving at a relatively low speed so there is minimal risk of transmission damage under low lube conditions.